The portal / The planetarium
Universum · Beneath the celestial domeThe sky.
The sky.
All around you.
Choose a location, move through the night and find celestial objects. A planetarium to explore, recognise and prepare your next observation.
5,044 stars · 88 constellations
The Sun, Moon and seven other planets.
A sky calculated for your viewpoint.
THE PLANETARIUMEXPLORE THE SKY / EDITION 01
Preparing the sky…Luxembourg · Europe/Luxembourg
Tonight’s skyCalculating positions…Natural lighting
Az. 180° · Alt. 28°Loading catalogue
Drag to turn, use the wheel or pinch to zoom. The “Day / night” button displays stars during the day too. Horizon graduations give azimuth in degrees and become finer as you zoom. The equatorial grid uses the equator and vernal equinox of the selected date; boundaries outline the 88 constellation regions. Tap an object for its fact sheet. With the sky focused, use the keyboard: arrows, + / −, Home to reset, Space to animate.
Times are calculated in UTC.STEREOGRAPHIC PROJECTION · HORIZON 0°
Your observing location and date
Three guides under the stars.
Turn your view
Azimuth starts at north: 0° north, 90° east, 180° south and 270° west. Altitude runs from 0° at the horizon to 90° at the zenith, directly overhead.
Watch the sky turn
Start animation at 3,600× to see an hour pass every second. Earth’s rotation changes celestial objects’ apparent positions through the night.
Prepare your outing
Select the Moon, a planet or a Messier object to open the planner at the same location and time. Then add your memories to the observing log.
What the planetarium calculates.
Positions, dates and horizon
Catalogue stars are positioned from their J2000 coordinates, with precession and nutation. The Sun, Moon and planets are calculated with Astronomy Engine from the selected location in topocentric coordinates. Altitudes are geometric, without atmospheric refraction. The ground represents a flat horizon at 0°; it reproduces neither terrain nor buildings.
The available period is 1900–2100. Stellar proper motion, parallax and aberration corrections are not modelled. Messier positions use the portal’s rounded coordinates. The planner applies its own refraction model: a small altitude difference near the horizon is normal.
Brightness, atmosphere and object size
The visual atmosphere evokes day and twilight based on the Sun’s altitude. It is neither a weather forecast nor a light pollution model. Stellar colours are illustrative, based on their B−V index; magnitude controls their symbolic brightness.
The Sun and Moon discs have a minimum size to keep them easy to locate. Planets, Saturn’s rings and Messier markers are enlarged symbols. The Moon’s illuminated fraction is calculated; its crescent points towards the Sun in the view. Displayed sizes cannot be used to compare their actual dimensions.
The portal’s night mode changes colours. Results describe a theoretical sky; actual observations depend on your horizon and conditions at the time.
Sources and credits
- d3-celestial, Olaf Frohn : snapshot dated 19 October 2026, 5,044 stars up to magnitude 6 and constellation lines and boundaries, in J2000 coordinates. Three-clause BSD licence. Astrometry and photometry: Hipparcos ESA 1997, retrieved directly from I/239; additional Gaia DR3 parameters, ESA/Gaia/DPAC · CC BY-NC 3.0 IGO. Names and designations: Kostjuk (2002), Smith (1996), Samus et al. and Gliese et al. indexes, referenced by d3-celestial. Translations from the sky culture tables are not included.
- Astronomy Engine, Don Cross, version 2.1.19: ephemerides, celestial frames and rotations. MIT licence.
- NGC catalogue: OpenNGC · Mattia Verga, CC BY-SA 4.0. 8,373 entries, including targets that can be searched for and selected in the sky. J2000 coordinates and symbolic markers.
- Messier objects: Steve Cimolino’s catalogue, NASA HEASARC and OpenNGC, Mattia Verga, coordinates adapted under CC BY-SA 4.0. Planner sources.
- Cities, approximate elevations and time zones: GeoNames, retained extract dated 18 October 2026, CC BY 4.0. Local time conversion: browser time zone database.
An independent creation for Universum · Steve Cimolino. Inspired by the open sky exploration offered by planetarium software; no affiliation with Stellarium. The sky is rendered using data retained on this site, without an external mapping service.
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